Institute of Electrical and Electronics Engineers (IEEE) 802.11 is a set of physical and Media Access Control (MAC) specifications for implementing wireless local area network (WLAN) communications. These specifications provide the basis for wireless network products using the Wi-Fi brand managed and defined by the Wi-Fi Alliance. The specifications define the use of the 2.400-2.500 GHz as well as the 4.915-5.825 GHz bands. These spectrum bands are commonly referred to as the 2.4 GHz and 5 GHz bands. Each spectrum is subdivided into channels with a center frequency and bandwidth. The 2.4 GHz band is divided into 14 channels spaced 5 MHz apart, though some countries regulate the availability of these channels. The 5 GHz band is more heavily regulated than the 2.4 GHz band and the spacing of channels varies across the spectrum with a minimum of a 5 MHz spacing dependent on the regulations of the respective country or territory.
WLAN devices are currently being deployed in diverse environments. These environments are characterized by the existence of many Access Points (APs) and non-AP stations (STAs) in geographically limited areas. Increased interference from neighboring devices gives rise to performance degradation. Additionally, WLAN devices are increasingly required to support a variety of applications such as video, cloud access, and offloading. Video traffic, in particular, is expected to be the dominant type of traffic in WLAN deployments. With the real-time requirements of some of these applications, WLAN users demand improved performance.
In a task group called IEEE 802.11ax, High Efficiency (HE) WLAN standardization is under discussion. The HE aims at improving performance felt by users demanding high-capacity and high-rate services. The HE may support UL and DL MU simultaneous transmissions, which includes Multi-User Multiple-Input Multiple-Output (MU-MIMO) and Orthogonal Frequency Division Multiple Access (OFDMA) transmissions.
When an AP transmits a data frame to a STA during a DL MU transmission, the AP may solicit an immediate acknowledgement from the STA. For example, the AP may solicit an immediate acknowledgement from the STA by setting the ACK Policy field of the data frame to a binary value of ‘00’. According to current IEEE 802.11 specifications, setting the ACK Policy field in this way solicits an immediate acknowledgement from a STA in an SU manner.
The AP may transmit a DL MU physical layer (PHY) Protocol Data Unit (PPDU) eliciting STAs to provide acknowledgements. The STA may transmit an immediate ACK, transmit a delayed ACK, transmit the ACK in an SU manner, and transmit the ACK in an MU manner. If multiple STAs transmit ACKs using the same transmission resource (e.g., at the same time and frequency resource), it may cause collision.